28 research outputs found
Seasonal variation of radial brightness contrast of Saturn's rings viewed in mid-infrared by Subaru/COMICS
Aims. To investigate the mid-infrared (MIR) characteristics of Saturn's
rings. Methods. We collected and analyzed MIR high spatial resolution images of
Saturn's rings obtained in January 2008 and April 2005 with COMICS mounted on
Subaru Telescope, and investigated the spatial variation in the surface
brightness of the rings in multiple bands in the MIR. We also composed the
spectral energy distributions (SEDs) of the C, B, and A rings and the Cassini
Division, and estimated the temperatures of the rings from the SEDs assuming
the optical depths. Results. We find that the C ring and the Cassini Division
were warmer than the B and A rings in 2008, which could be accounted for by
their lower albedos, lower optical depths, and smaller self-shadowing effect.
We also find that the C ring and the Cassini Division were considerably
brighter than the B and A rings in the MIR in 2008 and the radial contrast of
the ring brightness is the inverse of that in 2005, which is interpreted as a
result of a seasonal effect with changing elevations of the sun and observer
above the ring plane.Comment: 8 pages, 6 figures, accepted for publication in Astronomy &
Astrophysic
Formation and accretion history of terrestrial planets from runaway growth through to late time: implications for orbital eccentricity
Remnant planetesimals might have played an important role in reducing the
orbital eccentricities of the terrestrial planets after their formation via
giant impacts. However, the population and the size distribution of remnant
planetesimals during and after the giant impact stage are unknown, because
simulations of planetary accretion in the runaway growth and giant impact
stages have been conducted independently. Here we report results of direct
N-body simulations of the formation of terrestrial planets beginning with a
compact planetesimal disk. The initial planetesimal disk has a total mass and
angular momentum as observed for the terrestrial planets, and we vary the width
(0.3 and 0.5AU) and the number of planetesimals (1000-5000). This initial
configuration generally gives rise to three final planets of similar size, and
sometimes a fourth small planet forms near the location of Mars. Since a
sufficient number of planetesimals remains, even after the giant impact phase,
the final orbital eccentricities are as small as those of the Earth and Venus.Comment: 36 pages, 9 figures, 1 table, Accepted in Ap
How common are Earth-Moon planetary systems?
The Earth's comparatively massive moon, formed via a giant impact on the proto-Earth, has played an important role in the development of life on our planet. Here we study how frequently Earth-Moon planetary systems occur. We derive limits on the collision parameters that may guarantee the formation of a circumplanetary disk after a protoplanet collision that could form a satellite. Based on a large set of simulations, we observe potential moon forming impacts and conclude that giant impacts with the required energy and orbital parameters for producing a binary planetary system occur frequently with more than one in ten terrestrial planets hosting a massive moo
From planetesimals to terrestrial planets: N-body simulations including the effects of nebular gas and giant planets
We present results from a suite of N-body simulations that follow the
accretion history of the terrestrial planets using a new parallel treecode that
we have developed. We initially place 2000 equal size planetesimals between
0.5--4.0 AU and the collisional growth is followed until the completion of
planetary accretion (> 100 Myr). All the important effect of gas in laminar
disks are taken into account: the aerodynamic gas drag, the disk-planet
interaction including Type I migration, and the global disk potential which
causes inward migration of secular resonances as the gas dissipates. We vary
the initial total mass and spatial distribution of the planetesimals, the time
scale of dissipation of nebular gas, and orbits of Jupiter and Saturn. We end
up with one to five planets in the terrestrial region. In order to maintain
sufficient mass in this region in the presence of Type I migration, the time
scale of gas dissipation needs to be 1-2 Myr. The final configurations and
collisional histories strongly depend on the orbital eccentricity of Jupiter.
If today's eccentricity of Jupiter is used, then most of bodies in the
asteroidal region are swept up within the terrestrial region owing to the
inward migration of the secular resonance, and giant impacts between
protoplanets occur most commonly around 10 Myr. If the orbital eccentricity of
Jupiter is close to zero, as suggested in the Nice model, the effect of the
secular resonance is negligible and a large amount of mass stays for a long
period of time in the asteroidal region. With a circular orbit for Jupiter,
giant impacts usually occur around 100 Myr, consistent with the accretion time
scale indicated from isotope records. However, we inevitably have an Earth size
planet at around 2 AU in this case. It is very difficult to obtain spatially
concentrated terrestrial planets together with very late giant impacts.Comment: 51 pages, 19 figures, 2 tables, published in Icaru